let l = [("Don", 435.);("Nut", 75.);("Toto", 42.)];;

let rec find c l = match (c,l) with 
    (cl, []) -> failwith "Le client n'a pas ete trouve"
  | (cl, (n, c)::l) -> if  (String.lowercase cl) = (String.lowercase n) then
                               c
                       else find cl l;;

find "nut" l;;

